The effectiveness of dry powders in extinguishing fires has been known for some time. Sodium bicarbonate, potassium bicarbonate, and potassium salt are some powders that have been used in fire extinction systems. Silicone may be added to the dry powder to aid in the powder's free flow. Even silicone alone has been used electively as a dry powder to extinguish fires.
The use of dry powder has at least two significant disadvantages. Dry powder is difficult to spray for any distance. Thus, the spraying nozzle must be drawn much closer to the fire itself. Further, a fire extinguished by powder has a definite propensity to reignite under common circumstances. If a three dimensional fire, in particular, has burned long enough to heat elements in its environment, such as metals, although the powder may extinguish the fire, it is likely to reignite when the powder dissipates.
The term two dimensional (or static) fire is used herein to indicate the combustion of a non-replenishing fluid or solid. An example of a two dimensional fire is the burning of a tank or pond that is not, or at least is no longer, being fed from a remote source. The term three dimensional (or dynamic) fire, by distinction, is used to refer to a fire that is fed by a remote replenishing source. A well blow out and a burning tanker (the burn area being fed by fluid from within) are examples of three dimensional, dynamic fires.
Dry powder is particularly useful in extinguishing a three dimensional fire. Liquids and liquid foam mixtures are particularly useful in extinguishing static, two dimensional fires, as well as in cooling and reducing the size of three dimensional fires. It is quite difficult, however, with liquid and liquid foam mixtures alone, to extinguish a three dimensional fire. The alternating use of powders and liquids on fires has been attempted. The difficulty with this technique is the degree of coordination required and the close approach to the fire required for the powder nozzle.
The present invention discloses a method and apparatus for applying simultaneously dry powder and liquid, or a liquid foam mixture, to a fire. The method and apparatus is particularly useful for the extinction of three dimensional fires, together with their associated static fires. The method and apparatus achieves not only the advantage of permanently extinguishing a three dimensional fire but also the enhanced safety of permitting operation from a greater distance by extending the distance over which dry powder can be effectively sprayed.